This invention relates to the field of memory systems of the optimized or compressed data type--especially as used in data imaging.
Radar warning receivers have become an essential tool in the electronic warfare countermeasures art. As currently used, a radar warning receiver provides digitized signals representing the radio frequency spectrum location, the time of arrival, and other identifying data with respect to signals received from a distal radar transmitting apparatus.
A RWR (Radar Warning Receiver) field-of-view emitter environment can often consist of more than a thousand emitters with a combined density of several million PDW's (Pulse Descriptor Words) per second. Currently used RWR arrangements use pulse by pulse data processing techniques to generate a meaningful image from this type of input. FIG. 1 is an elementary block diagram of such a current RWR system. The RF (Radio Frequency) signal at 104 in FIG. 1 is encoded by the RF receiver 100 into PDW's which are sent along the path 106 to the system processor 102 where they are processed pulse by pulse and sent at 108 to the user. Pulse by pulse processing techniques rely on matching a number of pulse characteristics such as RF, AOA (Angle Of Arrival), TOA (Time Of Arrival) etc., with one another, then computing the PRI (Pulse Repetition Interval) for stable emitters or the range and characteristics for RF and PRI agility emitters. For the pulse by pulse processing approach, however, missing and/or corrupted PDW's significantly complicate the problem of deinterleaving trains of pulses. Even in low density environments many pulses are often missed due to, for example, time overlap of two or more pulses received by the RWR. As the density of the environment increases, the percentage of missed and corrupted pulses can be expected to increase causing the RWR system to detect and identify many more emitters (false alarms) than are present in the environment or falsely identifying emitters in chaotic system operation and breakdown in system performance.
The histogram processing approach, however, is far less sensitive to missed and corrupted pulse measurements and when used with other techniques can provide reliable RWR system performance even in dense emitter environments. The histogramming approaches currently considered for RWR systems are, however, limited to low resolution histograms of RF and AOA and are largely used as presorters for conventional pulse by pulse processing techniques. This approach is to use the histogram to store a number of PDW's per RF/AOA cell. The histogram is used to keep track of the number of PDW's stored. When the number of PDW's reach a given number (e.g., twenty), the file of PDW's is processed using the conventional pulse by pulse processing approach.
AOA tends, however, not to be a desirable sorting parameter due to poor measurement accuracies. The bin data is still processed pulse by phase and therefore the problems associated with pulse by pulse processing are still present after such sorting. Processing the RF/AOA histogram itself as a low level image and using this information to determine the makeup of the emitter environment offers a significant improvement of the sorting, however.
A simplified block diagram of a RWR system with histogrammer is shown in FIG. 2. Histograms in the FIG. 2 system are small and usually include between 128 and 1024 pixels for the RF axis and 128 pixels for the AOA axis with the PDW count comprising the Z-axis. A histogram size ranging from 16,384 to 131,072 pixels or memory words is considered feasible and within the current state-of-the-art.
Efforts to extend the histogramming approach to RF and TDOA (Time Difference of Arrival) organized data have proven difficult and also suggest the present compressed memory histogrammer concept. Two major aspects of these difficulties are concerned with the amount of memory required to accomplish a meaningful histogram from the RWR and the time required to transfer the contents in the memory to a processor. A more detailed and exemplary description of this memory requirement consideration is presented in the detailed description portion of the present document appearing below.
The patent art indicates the presence of inventive consideration of radar image processing systems and their memories. Included in this patent art is U.S. Pat. No. 4,851,854 issued to E. M. Drogin and concerned with a memory intensive image sorter system. Although the Drogin apparatus is concerned with real time loading of a ram memory and the use of pixel identification parameters as addressed in the memory loading arrangement, the present invention is distinguished histogram organization of the stored data. The additional U.S. Pats. of K. R. Jenkin, U.S. Pat. No. 4,721,958, concerning a real time pulse processor; R. J. Inkol, U.S. Pat. No. 4,879,561, concerning a filter system for radar applications; and F. Jehle et al, U.S. Pat. No. 4,891,648, concerning an aircraft radar arrangement are also of general background interest with respect to the present invention.